There has been an increasing recognition throughout the world that highway traffic is becoming an increasing problem, both from the standpoints of highway congestion and safety. One solution to this problem is to dramatically increase the number of highways to thereby decrease highway congestion. However, considerable expense is associated with the development of new highways and such new highways demand that an increasing percentage of land be utilized to support such highways, thereby decreasing the efficiency of a society's land utilization. Furthermore, in congested areas, there is little realistic opportunity to construct new highways, as no additional space exists. Accordingly, there is a need to make current highways more efficient.
There have been several recent proposals to develop an intelligent highway system which would allow both increased highway safety and higher highway utilization. One proposal for such an intelligent highway system is to automatically monitor and control the position of each vehicle along the highway, enabling the control of vehicle following distances and braking profiles to increase highway safety while reducing the vehicle spacing requirements otherwise necessary with individual vehicle operator control.
In such automated highway systems, it is desirable for the roadway and/or each vehicle to monitor the vehicle's longitudinal and lateral position along the roadway. Further, in such systems, automated lane tracking may be considered desirable. In such automated highway systems, it is further desirable to supply each vehicle and the operator thereof with highway originated information of various types. For example, it may be desirable to provide the operator of each vehicle with traffic jam information, regulatory information, as well as road direction and parking information.
A supplemental advantage of such an intelligent transportation system is that, through interactive control of each vehicle by the highway, less acceleration and braking inputs are necessary, reducing the amount of stop and go traffic and additionally reducing fuel requirements and according decreasing resultant pollution.
One such automated highway system which has been proposed is under development primarily, for example, by Nissan Motor Company, Limited with the policy support of the Japanese Ministry of Construction. Such a system determines a vehicle's lateral placement along the roadway through the use of magnetic nails imbedded down the center of the road bed and monitored by a vehicle born magnetic nail sensor which determines the relative position of the vehicle with respect to the magnetic nails, and seeks to control vehicle position to center the vehicle over the magnetic nails.
In the magnetic nail lateral position measurement system, the magnetic nails have the ability of being locatable virtually anywhere. However, the ability to monitor such magnetic nails is subject to severe degradation and depends on weather conditions. For example, a snowstorm may make such a lateral position measuring system unusable. Further, the use of such magnetic nails increases the complexity of roadway maintenance. For example, roadway resurfacing encounters significant difficulties when imbedded magnetic nails are present.
In the above-mentioned system, vehicle position longitudinally along the roadway is determined through the use of a global positioning satellite system (GPS). Each vehicle receives GPS signals and decodes them to determine the vehicle's own position. Such a GPS recorded position is integrated with velocity, acceleration, and yaw rate vehicle mounted sensors to produce a real time kinematic estimate of vehicle position. In such a kinematic-GPS system, while accurate longitudinal position of the vehicle may be developed, the GPS signals are not available under trees, bridges, or in tunnels, thereby limiting system usability.
The above-mentioned system further utilizes a road-to-vehicle communication system which comprises a vehicle mounted antenna communicating with a leakage coaxial cable installed along the roadway shoulder. However, this communication system must be installed separately from the above-mentioned systems, thus adding to expense.